Many millions of houses and small buildings located in hurricane or tornado risk areas are at high risk of damage from the strong winds of hurricanes or tornadoes. Recent studies of hurricane damage indicate that the most extensive damage to a house occurs when the roof is torn off, allowing the rain which often accompanies strong winds to ruin the contents of the house, and often allowing walls to collapse.
There is a great need for affordable retrofitting methods for reinforcement of the connection of wooden roof frames to underlying walls. While prior art connectors of steel strip tie-down types excel as affordable connectors of roof structures to underlying walls in new construction of houses and small buildings, they are not as applicable to retrofitting of existing roof frame structures. Such connectors pose difficulties in retrofitting applications because an upper portion of the steel-strip tie should extend over the top of a rafter/truss and down the other side in order to ensure adequate tie-down strength, by applying the restraining force mainly at the top of the roof frame as compression across the grain, which wood withstands quite well. If the tie-down connectors are simply nailed into the side of the rafter/truss, as is common in the prior art, localized tensions are induced across the grain of the wood such that the rafter/truss member tends to split under high uplift pressures, which can release the connector's nails. This weakness is of special concern in the southern part of the U.S. “hurricane belt”, where roof slopes are typically low, which both exacerbates wind uplift forces while subjecting the wood to tension more directly across the grain.
The over-the-top method is now widely recommended or required in the “Hurricane Belt” of the United States, even for retrofits of existing buildings. During retrofitting however, accessing the top portion of the rafter/truss requires removal and re-installation of an area of roofing and sheathing, which are laborious and costly operations, and as such, tend to discourage such retrofit upgrading of existing housing and building stock.
Prior art efforts to devise retrofits for reinforcement of roof structures have also been made. A number of United States patents as examples of such efforts are briefly discussed below.
In U.S. Pat. No. 5,257,483 (Netek) discloses some of the complications of retrofitting by installing anchor points in fascia and the wall below, allowing temporary placement of ties in the event of an impending storm. Winger, in U.S. Pat. No. 5,319,816, and several other inventors, disclose various temporary arrangements of multiple cables or nets over the roof which are anchored to the ground. Such temporary devices demand that the householder be at home and ready to react to storm warnings quickly and competently.
In U.S. Pat. No. 5,311,708, Frye shows a retrofit roof tie-down method in which lag screws are installed upwardly through an angled steel plate into the lower edges of the rafter/trusses, a lower leg of the angled steel plate being lag-screwed into the underlying wall. Frye's lag screws into the narrow edge of the rafter/truss however invite splitting and cause tension failure. Furthermore, only the screws near the junction of rafter/trusses with the top of the wall would contribute effectively, and the usual absence of a stud directly under a rafter/truss would leave Frye's wall lag screws rather ineffective.
Thompson, in U.S. Pat. No. 6,763,634, tries to resolve the retrofit problem by inserting ties down through the roofing and sheathing from above, with one strip on each side of the rafter/truss to form a saddle across it, which is able to effectively hold down the roofing and sheathing together with the rafter/truss. Thompson's ties extend down to connect to the underlying wall below. All this entails laborious and uncertain sealing of the roof penetrations, and interferes with any subsequent re-roofing job.
Therefore, there is a need for an improved retrofitting apparatus and method for reinforcement of roof frame structures.